Why do our early interactions, particularly those with our parents, have such an enormous impact on subsequent social behavior and how we rear our own children? There is overwhelming and unequivocal evidence that aberrant parent-offspring interactions during early life, including maltreatment and abuse, negatively impact adolescent behavioral outcomes and perpetuate a continuing cycle of abuse or maltreatment. However, there are few, if any, studies that have directly linked these early experiences to changes in brain organization and connectivity. Further, the underlying genetic and epigenetic mechanisms present during development that generate these anatomical changes to the brain are only poorly understood. The overarching goal of this proposal is to determine how early social interactions, mediated by somatosensory and olfactory systems, impact the development of specific patterns of connectivity to produce individual differences within a population. We use a unique animal model, the prairie vole, which is one of only a small proportion of mammals that are monogamous, pair-bonded and that rear their young bi-parentally. Pair-bonded parents show remarkable variability in rearing styles, particularly in behaviors requiring close physical contact such as nursing, huddling, and non-huddling contact, all of which profoundly shape tactile and olfactory experience. We have quantified these differences in rearing style, and have demonstrated significant differences in cortical connectivity and social behaviors of the offspring of high contact (HC) and low contact (LC) parents. In addition, LC and HC offspring adopt a similar rearing style to that of their parents, perpetuating these two distinct phenotypes. Cross-fostering of offspring demonstrates that these changes in behavior are culturally transmitted rather than inherited. This opens up the intriguing possibility that, in large part, experience generates the differences in cortical connectivity associated with the different behaviors. In othe words, some aspects of brain organization may be culturally transmitted. However, a direct relationship between differential sensory experience, parental rearing styles, and cortical connectivity of the brain has never been established. In humans, rodents and many other mammals, early tactile and olfactory experience is critical for forming filial relationships betwee the mother and the offspring and for establishing normal social behavior later in life. Thus, results from our studies in voles have broad implications for mammals in general, including humans. In these studies we will cross-foster HC and LC offspring; in some of these litters we will induce anosmia. In all groups we will compare cross-fostered offspring with their in-fostered siblings and their biological siblings on several measures including: olfactory and tactile discrimination, social behavior, and density and distribution of connections of somatosensory (S1), olfactory (orbitofrontal cortex, OFC), and anterior cingulate (ACC) cortical areas. Finally, we will determine the period in development when alterations in connectivity occur, and explore some of the genetic and epigenetic mechanisms that drive these changes in cortical connectivity. With this design we will reveal the mechanisms that translate early sensory experiences into a cortical phenotype that generates adaptive, and complex social behavior later in life.